Field
Exemplary embodiments of the present disclosure relate to a light emitting diode and a light emitting module, and, more particularly, to a high-power light emitting diode capable of operating at a high current density and a light emitting module including the same.
Discussion of the Background
In general, with good thermal stability and a direct transition type energy band structure, Group III-based nitrides, such as gallium nitride (GaN), aluminum nitride (AlN), and the like, have been spotlighted as materials for light sources in the visible range and the ultraviolet range. In particular, blue and green light emitting diodes using indium gallium nitride (InGaN) are used in various fields including large natural color flat displays, signal lamps, interior lighting, high density light sources, high resolution output systems, optical communication, and the like.
Typically, a heterogeneous substrate having a similar crystal structure to a nitride semiconductor layer has been used as a growth substrate for growth of the nitride semiconductor layer due to difficulty in fabrication of a homogeneous substrate capable of growing such Group III-based nitride semiconductor layers. In particular, a sapphire substrate having a hexagonal crystal structure is generally used as the heterogeneous substrate. In recent years, a technique has been developed for manufacturing a high efficiency vertical type light emitting diode, in which epitaxial layers such as nitride semiconductor layers are grown on a heterogeneous substrate, such as a sapphire substrate, and a support substrate is bonded to the epitaxial layers, followed by separating the heterogeneous substrate through laser lift-off or the like.
However, the epitaxial layer grown on the heterogeneous substrate has a relatively high current density due to lattice mismatch and difference in coefficient of thermal expansion between the epitaxial layer and the growth substrate. In general, an epitaxial layer grown on a sapphire substrate is known to have a current density of 1E8/cm2 or more. With such an epitaxial layer having high current density, a light emitting diode has a limit in improvement in luminous efficacy.
Moreover, in order to reduce manufacturing costs of a light emitting diode, there is a need to increase the quantity of light emitted from the light emitting diode per unit area. To this end, the light emitting diode is required to operate at high current density. However, in operation at high current density, the light emitting diode suffers from a severe drooping phenomenon due to current crowding through dislocations than in operation at low current density, thereby causing severe deterioration in internal quantum efficiency. In addition, since the epitaxial layer grown on the heterogeneous substrate has a very thin thickness of several micrometers, as compared with a light emitting area of, for example, 350 μm×350 μm or 1 mm2, the light emitting diode undergoes difficulty in current spreading in the horizontal direction and thus suffers from further deterioration in luminous efficacy with increasing current density.
Moreover, in operation at high current density, the light emitting diode generates a significant quantity of heat, causing increase in junction temperature thereof. Typically, the light emitting diode has a maximum junction temperature (Max Tj) of 150° C. or less. However, in order to use such a light emitting diode at a high current density of 150 A/cm2 or more, there is a need for a particular cooling system for preventing increase in junction temperature.